third age

Noun

UK uncountable

(UK) The age after retirement but while one is still young enough to be active; young old age.

Japanese Meaning

退職後でありながら、まだ活動的でいられる高齢期 / 活力を保ちながら過ごすセカンドリタイア（初老期）とも言える年齢層

Many people find new hobbies and social groups during the third age.

多くの人がリタイア後の活動的な時期に新しい趣味や社交グループを見つけます。

Sense（1）

(UK) The age after retirement but while one is still young enough to be active; young old age.